The present invention relates to a method of curing preferably so called osmosis which may exist in practically all objects manufactured from plastic laminates. When osmosis is noted to such an extent that the objects are damaged, this is normally referred to as that the objects have been hit by bubonic plague, plastics plague, glass fiber hull plague or osmosis. This latter term will be used hereinafter.
One type of object that is frequently exposed to osmosis is a plastic boat. See for instance Batnytt 10 September 1990, pages 28-31. Therefore, the description below will refer to the treatment of boats, although it is generally applicable.
It is not clear why osmosis does not occur always, or why a chemical acid generating process starts in some cases but not in other cases. However, it is clear that osmosis in many cases is a big problem.
It has been speculated that the reason for osmosis is that there might be some constituents of the water that are active and that the bottom paint or dust that has contaminated the surface of the object during the manufacture functions as a catalyst.
The damages manifest themselves in that the acid, in addition to forming gas blisters outwardly, also corrodes inwardly. The size of the gas blisters gives no sure indication of how big the damage is that is concealed within the hull. The extent of the damage will be evident only when these have been exposed.
In order to cure damages resulting from osmosis it is necessary:
1. to localize all the damaged areas;
2. to expose the damage;
3. to remove both the formed acid and the damaged laminate material;
4. to clean up and dry out;
5. to build up the laminate to the original hull thickness and strength; and
6. to restore the hull on the outer surface by means of a water tight layer, such as a gel coat or a high molecular weight epoxy.
It is known that it is possible to use drying equipment of hyper absorption type, in the following referred to as hyab-equipment, for effectively drying laminate that has been made moist, such as at blasting or washing. See for instance, Batnytt, 10 September, 1990 page 29. This article refers to drying by means of the hyab-equipment as "hyper drying by means of compressed air and bottle gas heat".
The hyab-equipment uses compressed air and bottled gas in combination with each other and the drying medium consists of a dry, hot air flow that sweeps along the object at a high velocity.
The drying method of the hyab-equipment is based on the fact that the moisture is effectively removed from an object, in that the surface thereof is cooled by the evaporation of the moisture and that the moisture within the material according to the "law of the cold wall" is urged to move towards the surface thus cooled, where it is dried. Conversely, heat directed to the surface of an object urges the moisture deeper into the material. See for instance the HYAB-Comparison.
A visual localization of the damaged areas is not only time-consuming but may, indeed, be impossible to carry out, particularly if a hull has been standing on land for some time and has dried out, because the usually only small sized blisters have dried out and are no longer visible.
Despite this, particularly in hotter climates, a conventional method is to cure osmosis only when the hulls have been standing on land for an extend period in order to dry out. This timely extended method not only renders the localization of damages difficult but makes the whole curing of osmosis unnecessarily expensive. Yard rentals for storing the boats for an extended period of time, expenses for a continuous check of the moisture content of the hull, and the fact that the boat is not available for its intended purpose, are costs that may be reduced or eliminated entirely through practice of the present invention.
The object of the present invention is to quickly and effectively localize and cure damage due to osmosis.
The method encompassed by the present invention goes considerably further than the known drying technique which is utilized at first when the damaged areas have been localized and exposed.
By using, within the scope of the present invention, the temperature stability which characterizes the hyab-equipment, i.e. also by the higher temperatures that are not useful for drying, it is possible, without the harmful effects that may be the result of a heating by means of bottle gas burners only, to localized also damages in a hull that are concealed to the eye. Due to this, it is possible to advantageously directly treat wet objects, such as "sea-wet" boats, which gives the method a considerable advantage in time and thus savings.
This temperature stability may thus be utilized to not lastingly exceed the temperature up to 300.degree. C., which insurance companies now for risk of fire reasons prescribe, for example, for hot jobs on roofs. Characterizing for the fire security at jobs with a hot compressed air jet is that, if an inflammable material should be put on fire, then extinguishing will be caused by the air jet if it is quickly placed at a somewhat increased distance, or is cooled by an immediate shut-off of the heat in that the air jet blows out the flame. When the heat admission is switched off entirely, the air jet acts strongly cooling, which means that there, due to the invention, is always available an effective fire extinguishing and cooling medium at the job site.
One type of tool that may be used for the method according to the invention is, for instance the HYAB-osmosis tools, which basically correspond to the known drying tools but which, among other things, are adapted for an immediate switching between heating and cooling functions.
However, by the method according to the invention it is achieved not only that the damage is localized, but also that evaporated acid and gases build up a pressure, that from inside breaks up the superposed material.
The combination of controlled comparatively strong heat or cooling, respectively, with a mechanical action by the strong compressed air jet makes it possible to clean the damaged area from both acid and eliminate damage in one operation. The need for sand blasting methods, both wet and dry, which due to environmental considerations are not possible to use within all yard areas, are eliminated through the invention.
Considerable savings are, beyond the time gain with respect to the treatment course, that the costs for blasting material and the removal thereof are eliminated, and that the hull need not be covered.
Other disadvantages of the known blasting methods are that they are effective, but simultaneously coarse, methods which, due to the difficulties of visually determining the existence of damage, are often utilized for the whole hull rather than limiting the destroying action of the blasting to only the damaged areas. Thus, by sand blasting, where it can be utilized at all, it should be noted that it is often times too efficient and, by its destroying action, may result in damage and considerable unnecessary work with, among other things, application of several replacing layers of glass fiber reinforcement in order to restore the original thickness and strength of the hull.
A general drawback inherent with all blasting is that the laminate becomes uneven and has to be built up anew in order to reach its original strength and smoothness. Due to the coarse operation of the blasting this rebuilding to original smoothness becomes time and material consuming, which results in unnecessary high costs.
By hull treatment within the scope of the invention the efforts may, as already mentioned, be concentrated to the localized areas where damage is to be found. Between the cured areas there are left intact and untouched areas that denote the original shape of the hull, prior to the curing. With these intact areas as templates, the restoring job is easier and the material consumption is reduced.